Many current electronic products rely upon low-power or battery-powered operation of one or more integrated circuits (ICs). These integrated circuits can be used in a wide variety of low-power or battery-operated applications including, for example, mobile phones, smart watches, sensing applications, or other low-power or battery-operated devices or applications. For many low-power ICs, an external voltage (e.g., battery) is converted to a lower voltage and regulated on-chip using a DC-DC converter that operates using switched output drivers that control power switches to control energy storage and release to reactive components. The DC-DC converters are controlled to maintain an output voltage that is provided to a load on the integrated circuit.
Compared to a linear regulator, a DC-DC converter, whether using capacitive or inductive reactive components, can achieve a higher power efficiency, especially for large differences between the higher input voltage and the lower output voltage. Compared to using capacitive reactive components, using an inductive DC-DC converter has the advantage that for varying input and/or desired output voltages, the desired output voltage can be maintained by changing the timing of how the power switches are controlled, instead of changing the voltage conversion topology as would be needed for a capacitive DC-DC converter. However, maintaining a good power efficiency at low output power still remains a challenge.
Applying burst-mode control has advantages because good power efficiency can be maintained over a large load-current range. In conventional burst-mode DC-DC converters, the voltage regulation control is designed such that the DC-DC converter only performs burst-mode switching when the output voltage drops below a certain defined low-voltage threshold. This minimizes the converter switching actions and increases efficiency, especially for low output power since the DC-DC converter only switches when really needed. For burst-mode DC-DC converters, a burst mode including one or more current charging cycles is performed by the DC-DC converter for a short period of time after detecting an output voltage below a low-voltage threshold. During burst mode, the DC-DC converter typically operates in continuous-conduction mode (CCM) with a controlled inductor current while ramping up the output voltage from a defined lower level to a defined upper level for a voltage regulation window. Thus, the output voltage of such a burst-mode DC-DC converter is controlled to be within the high-voltage threshold and the low-voltage threshold for the voltage regulation window.
For burst-mode implementations, the switching activity of the DC-DC converter increases with the load current. If the load current increases, the output capacitor for the DC-DC converter is drained faster. As soon as the low-voltage threshold of the voltage regulation window is reached, a burst is started. For high load conditions, an increased number of bursts with a longer duration are required because the load current subtracts from the inductor current during the burst. The resulting lower current into the output capacitor causes the output voltage to rise more slowly. Thus, the burst frequency and burst duration depend on the load current. Further, within the burst, output current is typically controlled to yield a certain average burst inductor current, for example by controlling the valley and peak currents. As soon as the high-voltage threshold is reached, the burst is ended and the DC-DC converter stops switching while the load draws current from the output capacitor until the low-voltage threshold of the voltage regulation window is again reached. At this point, the burst cycle repeats.
The switching action of burst-mode DC-DC converters during such burst modes can cause interference with sensitive circuits, such as analog signals, on an integrated circuit. For example, if an action by a sensitive circuit elsewhere in the system coincides with the switching action of the DC-DC converter during a burst mode, accuracy or performance of the action can be compromised. One example for such a sensitive action is the sampling of an analog input voltage by an analog-to-digital converter (ADC). If this sampling occurs during burst-mode switching for the DC-DC converter, accuracy of the ADC measurement can be degraded.